They went to a Red Crescent centre and spoke to doctors, opposition activists said.

On the video, which the BBC has not been able to fully authenticate, one resident is heard telling an inspector of heavy raids on the district, with "over 600 canister strikes...12 tanks, 100 soldiers".

Shortly after setting out from their hotel in Damascus, the inspectors' cars came under fire "multiple times by unidentified snipers", according to a statement from the UN.

Analysis

Whitehall officials say no firm decision is likely to be taken on how Britain will respond to last week's alleged chemical attack in Syria until at least Wednesday.

That is when UK PM David Cameron will be chairing a session of the National Security Council, attended by military and intelligence chiefs and senior ministers.

It follows intense consultations between London and Washington with Downing Street keen to stress the two countries are acting in concert.

Any military response, if it is decided on, is most likely to be confined to a one-off or limited guided missile strikes on selected Syrian military targets using Tomahawk cruise missiles fired from US Navy warships stationed hundreds of miles away in the eastern Mediterranean.

US vessels there are reported to have around 400 such missiles onboard, while a Royal Navy submarine in the region can also carry cruise missiles.

But Russia, Syria and Iran have all issued strong warnings against any western military action.

The team returned safely back to the government checkpoint before setting out again.

The convoy was "deliberately targeted" and it seemed someone was trying to intimidate the team, the UN Secretary General's spokesman, Farhan Haq, told the BBC.

The inspectors have now returned to their hotel and are expected to resume their work on Tuesday.

Military action

A year ago, US President Barack Obama said the use of chemical weapons by the Syrian government would be "a red line" that could trigger US military action.

Washington has recently bolstered its naval presence in the eastern Mediterranean, and military leaders from the US, UK and their allies are meeting in Jordan.

But the UN Security Council remains divided, with China and Russia appearing unlikely to drop their objection to stricter sanctions on Mr Assad's government.

Chinese Foreign Minister Wang Yi said on Monday that diplomats should be cautious in dealing with the chemical weapons issue, and Moscow warned Western nations not to prejudge the outcome of the inspections.

Western politicians have begun to suggest taking action outside of the UN system.

UK Foreign Secretary William Hague told the BBC that action could be taken without UN approval if there was "great humanitarian need" in Syria.

His French counterpart Laurent Fabius suggested the UN Security Council could be bypassed "in certain circumstances".

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But in his latest comments on the crisis, Russian Foreign Minister Sergei Lavrov said any intervention in Syria without a UN mandate would be a "grave violation of international law".

The West, he told a news conference in Moscow, had not been able to come up with any proof of chemical weapons use while "saying at the same time that the red line has been crossed and there can be no delay".

'Neurotoxic symptoms'

Western officials were unimpressed with Syria's decision to allow in the UN experts.

Mr Hague said evidence could have been tampered with, degraded or destroyed in the five days since the attack.

A senior White House official, quoted by AP news agency, dismissed the visit as "too late to be credible".

Medecins Sans Frontieres (MSF) said on Saturday that three hospitals it supports in the Damascus area had treated about 3,600 patients with "neurotoxic symptoms" on Wednesday morning, of whom 355 had died.

While MSF said it could not "scientifically confirm" the use of chemical weapons, staff at the hospitals described a large number of patients arriving in the space of less than three hours with symptoms including convulsions, pinpoint pupils and breathing problems.

BBC links

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